1. Field of the invention
The present invention relates to an apparatus for hoisting boats which may be used with any available lifting means and which is particularly suited for a mobile crane or for a quay crane.
2. Description of the prior art
Commonly, cranes used for hoisting small and mediumsized boats, typically pleasure boats such as speed boats and sail boats, to and from a quay, utilize a slinging structure formed by a balance frame of suitable dimensions constituted by a sturdy frame of rolled steel sections and having commonly an "H" shape, on the longitudinal beam member of which there is a ring for receiving the hook of the lifting crane. Slings, commonly of textile fibers, are passed under the bottom of the boat and hooked to the ends of the two crossbeams of the balance. A correct positioning of the two slings is crucial in order to ensure a safe trim of the boat when it is lifted out of the water or of the cradle and slings positioning is an operation made manually and often repeated for adjusting the trim after testing it by lifting the boat that much as to be able to judge whether the slings position is correct, before the boat can be lifted safely out of the water or out of the docking cradle. These manual operations require at least two persons and a relatively long time, thus limiting productivity on the quay.